Recording materials comprising electron-donating dye precursors and electron-accepting compounds are well known as pressure-sensitive recording paper, heat-sensitive recording paper, light-sensitive pressure-sensitive recording paper, electric heat-sensitive recording paper, etc.
Details of such recording materials are described in British Patent No. 2,140,449, U.S. Pat. Nos. 4,480,052 and 4,436,920, JP-B-60-23922 (the term "JP-B" as used herein means an "examined Japanese patent publication"), and JP-A-57-179836, JP-A-60-123556, and JP-A-60-123557 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
In particular, many processes and materials for heat-sensitive recording have long been known. For example, examples of heat-sensitive recording materials comprising electron-donating dye precursors and electron-accepting compounds are disclosed in JP-B-43-4160, and JP-B-45-14039. Examples of heat-sensitive recording materials comprising diazo compounds are disclosed in JP-A-59-190886, and JP-A-63-98485. Examples of heat-sensitive recording materials comprising a chelating compound formed of ferric stearate and gallic acid are disclosed in U.S. Pat. No. 2,663,654. In recent years, these heat-sensitive recording systems have been applied in a variety of fields such as the facsimile, printer and label fields and have been in growing demand.
As the demand for such heat-sensitive recording systems has grown, recording materials have been desired which can provide heat-sensitive recording at a higher rate and provide a sufficient density at a low energy. In recent years, since heat-sensitive papers have been used to form high picture quality images equivalent to that of silver salt photographs, a high picture quality heat-sensitive paper has been desired which can provide an improved dot reproducibility with respect to a printing head.
One approach for providing an improved heat-sensitive recording material there has been proposed in JP-A-63-116890, in which an interlayer comprising as main components a pigment and a binder is provided interposed between a heat-sensitive recording layer and a support so that the smoothness of the heat-sensitive recording material is improved to enable typing at a lower energy. Despite its contribution to some improved sensitivity, this material leaves much to be desired. This material cannot provide a sufficient desired sensitivity. This material cannot exhibit a sufficient running property. Thus, this material is not practical.